Why So Much Compost?

soccer_dadJune 5, 2008

I've read and cited the basic rule of thumb of 1 cu yard of compost per 1000 sq ft. But, I've never added that much compost at one time to my lawn. The last bag of compost I used, and actually read the application rate, the directions were 40#/500 sq ft.

I have mixed bagged compost with grains and spread over the lawn. I can't imagine spreading a cu yd/1000 of compost as a topdressing on growing grass. Maybe for a complete renovation.

Where did the 1yd/1000 rule come from?

What is the basis? Amount to increase OM a certain percentage or something like micro organism count.

My guess is that that rule of thumb came from the 1/4 to 1/2 inch of top dressing rule of thumb. If you calculate it out, 1 cu yd per 1000 sq ft comes to .324 inches deep, which is just a hair closer to 1/4 inch deep than to 1/2 in deep. More than 1/2 in deep and you risk choking the grass.

If you're fertilizing with grains, etc, you're adding plenty of OM, so the compost would only be needed to add microbes if your soil isn't healthy.

It not necessarily a hard fast rule. With any amendment, the objective is not to smother the existing grass, plant, etc. Compost applied @ 1/4-1/2" thickness on existing lawns seems to be perfect. Of course if your starting a new lawn from bare soil you could apply compost much heavier.

What is the basis? Amount to increase OM a certain percentage or something like micro organism count.

An application of compost will do much more for your soil than just populating it with microbes. The compost, along with feed grains will continue pass through the microheard over and over, gradually releasing nutrients, conditioning your soil and forming humus. Fungal strands and grass roots will grow deep increasing the biomass below the surface. Moisture and nutrient retention will increase as the greater biomass acts as a sponge soaking up moisture and nutrients, releasing them when needed.

There is no such thing as "THE RIGHT" amount of compost as long as you don't kill your existing lawn and you'd be surprised at how much top dressing your lawn will tolerate if its well watered in.

Rather than worry about amount I'd ask why you're looking to top dress in the first place. If you know for certain that your soil is grossly low in organic matter then it makes sense to go to the effort. Otherwise, especially if you're mulch mowing, I'd think long and hard about just brewing tea and spraying. Unless you really need an infusion of OM tea has all the benefits of compost, and then some, and is much much much easier to deal with.

Guys the discussion is about "why" the rule of 1 yd/1000. I understand the benefits, I understand why one wants added OM. I am challenging the posts from the regulars on this board that cite "add compost at a rate of 1 cu yd/1000."

My point is that not only is it expensive, it just may not be necessary when one is also adding clippings and meals. Perhaps a lesser amount is good too, easier for beginners to understand and still beneficial to the soil.

Can a lawn just starting out even digest that much compost in a season? Mine can't and I don't think compost on top of the soil structure is really doing much good. Shouldn't it be at the root zone for maximum effect?

I'm asking the questions to try to better understand the science behind the amount of compost and is that sound advice for folks just starting with an organic program. Though I tend to agree with decklap that there is no right answer just varying degrees of benefit.

soccer dad to be perfectly frank I would disregard that "rule or thumb". I've gotten lawns that have tested at If turf is doing well enough that over application is a potential issue then compost probably isn't your best choice. I know Im a broken record here but think about an app of tea.

All that said if you still wanna go that route consider aerating and top dressing over the plug holes to get the compost into the root zone.

I'm hoping others who use the forum for learning rather than just seeking an answer to a specific question will read this post. I too agree that if you want to use the 1 cu yd per 1000 that a good core aeration is best, especially when just starting out. It is also perfectly ok, to use some amount less that fits ones circumstances.

I've thought about the tea. When I plot out the time needed to brew and use, cleanup, etc... it just doesn't fit my schedule as well as just mixing some compost in with my grain applications. Others my find it works well for them.

Well soccer_dad, here's a little lesson to enrich you regarding one of your points:

Compost on top is great. Compost at the roots is great too.

On top: Worms will make the trip up to eat the compost (which involves bringing it down to their hidey holes for some exodigestion). While coming up they're aerating and leaving fertilizer in their poo. What they bring down can benefit that root zone.

Down low: creates pores, food, and some light nutrition fo your plants. If you tilled it in then it probably also has some of your sweat as you labored to do so :).

I like applying it on top and letting nature work it in, but I'm lazy.